1. Field of Invention
The present invention relates to a thin film transistor (“TFT”) substrate, and more particularly, to a TFT substrate in which an organic semiconductor layer is provided.
2. Description of the Related Art
A TFT substrate includes a TFT as a switching and driving device for controlling and driving the operation of each pixel. The TFT includes a semiconductor layer, and the semiconductor layer is generally formed of amorphous silicon or polysilicon. However, an organic semiconductor material has recently been substituted for the semiconductor layer.
Since organic semiconductor materials can be formed at room temperature and atmospheric pressure, they may provide a number of advantages. For example, the fabricating cost may be reduced, and the organic semiconductor material may be applied to a plastic substrate which is susceptible to heat damage. However, the organic semiconductor material has disadvantages as well; for example, it has low chemical resistance and plasma resistance.
An organic TFT including an organic semiconductor material as described above includes an insulating substrate, a gate electrode formed on the insulating substrate, a gate insulating film covering the gate electrode and formed of an organic material, source and drain electrodes which are separated by the gate electrode so as to define a channel area, an organic semiconductor layer formed in the channel area, a first passivation layer formed on the organic semiconductor layer, and a second passivation layer formed on the first passivation layer and containing aluminum.
However, since the organic TFT is composed of only a single layer of the gate insulating film, the gate insulating film may not provide sufficient insulation between the data wire and the gate wire. Due to such an insulation defect, the hysteresis width of the TFT is increased, and thus the organic TFT has poor reproducibility. Additionally, the second passivation layer (typically containing aluminum) has a large stress with respect to the first passivation layer on which it is formed, thereby causing an effect referred to as “lifting.” The lifting effect may also deteriorate the hysteresis characteristic of organic TFT structures.